Carbon-Coated Yttria Hollow Spheres as Both Sulfur Immobilizer and Catalyst of Polysulfides Conversion in Lithium-Sulfur Batteries.

Li-S battery has tremendous application prospect on account of the high theoretical specific capacity and large energy density, while its large-scale application is impeded by the severe shuttle effect and the slow electrochemical kinetics of polysulfides conversion. Herein, the Lewis acidic yttria hollow spheres (YHS) are rationally designed as both sulfur immobilizer and catalyst of polysulfides conversion for the advanced Li-S batteries. It can be known that the Lewis acidic yttria can effectively capture the Lewis basic polysulfides and thus mitigate the shuttle effect of Li-S battery; besides, yttria shows the enhanced catalytic effect for the kinetics of interconversion reaction from polysulfides to Li2S. As a result, either as a sulfur host or as the separator coating, yttria plays a vital part in realizing the high specific discharge capacity and good cycle stability for Li-S battery. In particular, Li-S battery with YHS@C/S cathode and YHS/CNT-0.6- modified separator (2.1 mg cm-2 active material loading) shows a good specific discharge capacity of 912.5 mAh g-1 at 0.5C. Even after 200 steady cycles, the discharge specific capacity can keep as 842.3 mAh g-1, and the capacity decay rate is only 0.038% per cycle. When active material areal loading is increased to 4.24 mg cm-2, it still maintains a considerable areal capacity of 3.79 mAh cm-2. In consequence, the synergy of polysulfides confinement and catalytic conversion reaction provides a meaningful exploration for achieving the high performance of Li-S batteries.